Antisense Peptide Nucleic Acid–Diaminobutanoic Acid Dendron Conjugates with SbmA-Independent Antimicrobial Activity against Gram-Negative Bacteria

Abstract

Precision antisense antibacterial agents may be developed into novel antibiotics in the fight against multidrug-resistant Gram-negative bacteria. In this study, a series of diaminobutanoic acid (DAB) dendrons are presented as novel carriers for the delivery of antisense antibacterial peptide nucleic acids (PNAs). The dendron–PNA conjugates targeting the essential acpP gene exhibit specific antisense antimicrobial bactericidal activity against Escherichia coli and Klebsiella pneumoniae at one-digit micromolar concentrations, while showing low toxicity to human cells. One compound selected from a structure–activity relationship series showed high stability in mouse and human serum ( t 1/2 ≫ 24 h) as well as in vivo activity against a multidrug-resistant, extended spectrum beta-lactamase-producing E. coli in a murine peritonitis model. The compound was also well tolerated in mice upon i.v. administration up to a dose of 20 mg/kg, and in vivo fluorescence imaging indicated clearance via renal excretion with slight accumulation in the kidneys and liver. Thus, DAB-based dendrons constitute a promising new chemistry platform for development of effective delivery agents for antibacterial drugs with possible in vivo use.

Selected strategies to fight pathogenic bacteria

“…Conversely, the corresponding guanidinylated derivatives exhibited MIC values in the ranges 0.25–2 µM and 0.125–8 µM against E. coli and K. pneumonia , respectively. The C 8 linker conferred highest activity, however, the mismatch PNA conjugate also possessed substantial activity (MICs of 4–8 µM) that appeared to arise from membrane-disruptive effects 63 . To assess the influence of the size of the core dendritic structure on antibacterial activity, two similar third-generation dendrons with a core of 2,3-diaminopropanopic (Dap) residues were examined as well.…”

“…Besides Arg-based modification of AMPs to obtain more efficient delivery vehicles for PNA, a recent work reports on guanidinylated dendrimeric delivery moieties for PNA targeting the translation of the acpP mRNA essential for fatty acid synthesis 63 . Based on a series of 2,4-diaminobutanoic acid (Dab)-based dendrons, the structure-activity relationships (SARs) were explored with respect to the effects of terminal guanidinylation as well as the length (and thus hydrophobicity) of the terminal linear cationic carbon linker (C 4 to C 8 ) moieties.…”

“…However, only slight differences in activity between the Dap- and Dab-based conjugates were observed, implying that the outer shell of the dendron is most important in determining the antibacterial properties of dendron-PNA conjugates. The guanidinobutanoyl-modified Dab-based dendron with a charge of +8 was subjected to further studies, which showed: (i) SbmA-independent activity, (ii) low cytotoxicity against the liver cell line HepG2 (full viability at 90 µM), (iii) MICs increased in the presence of high concentrations of divalent cations (Ca 2+ and Mg 2+ ), (iv) bactericidal mode of action, (v) high stability in mouse and human serum, with t 1/2 ≫24 h, (vi) in vivo activity against a multidrug-resistant E. coli in a murine peritonitis model 63 .…”

Unlocking the potential of chemically modified peptide nucleic acids for RNA-based therapeutics

“…To improve bacterial delivery, PNAs have been conjugated with diaminobutanoic acid dendrons to target the acpP gene, which exhibited bactericidal activity against E. coli and Klebsiella pnuemoniae at 0.5 M concentration 71 . Another strategy to improve the delivery of PNA is conjugation with vitamin B12 as it is an essential nutrient for bacteria 72 .…”

Artificial genetic polymers against human pathologies

“…In terms of numerous attempts to improve the delivery of AGPs into bacterial cells, one study has shown promise where diaminobutanoic acid (DAB) dendrons coupled to antisense PNA (anti- acpP ) demonstrated a low toxicity for cultured human cells simultaneously with good bactericidal activity against E. coli and Klebsiella pneumoniae [ 119 ].…”